Enthalpy

Please tell us the mirror diameter to provide power at the distance of a remote star. The Esa paper does not envisage it.

In the frame of refernce of the scales and mass, Earth is heavier because of its speed. And yes, I believe that rest mass and energy create gravitation, so that the moving Earth attracts the test mass more strongly. This includes kinetic energy, as already discussed there http://www.scienceforums.net/topic/74526-q-on-general-relativity/ Will you suppose that the aluminium tank takes a different orbit aroud the Earth than the carbon+hydrogen fuel it contains? These atoms have a rest mass consisting of varied proportions of kinetic energy at their electrons, which changes the atom's inertial mass.

Hi mriver8, welcome here! 1MHz is nothing special, neither for microphones (piezo elements) nor recorders (hard disk drive). The defining question is whether you consider ultrasound in air, and then 1MHz is really a lot, or in a liquid or solid, for which 1GHz would still be possible and existing technology.

MOS are excellent UHF preamplifiers (and mixers). They bring a low noise and a better linearity (against intermodulation and transmodulation) than bipolars. Using them is absolutely right. Impedance matching is done rather easily and well in VHF and UHF. Traditionally we used transformers, presently wideband LC circuits are more common. This permits the MOS to see the high source impedance it needs to be silent (its noise voltage is rather strong, but its noise current very small, so a transformer that multiplies the signal voltage makes a good signal-to-noise ratio). It also permits the source to see an impedance that matches itself more or less: not the several kohm of a dual-gate MOS input, but something like 40 ohm for a 75 ohm input. This permits good MOS preamplifiers to have a noise figure like 1.0dB or even less, which does indicate a proper matching. It also permits a MOS to amplify. Without impedance matching, 25mS transconductance with 50ohm input and output would result in nothing. Only the voltage gain at the input transformer, and the kohm load impedance at the drain, permit a MOS to amplify. The strong impedance transformation needed by a MOS is not obvious to obtain on a wide band like 470-860MHz. Software helps now. ---------- 75 ohm is the preferred impedance of a coaxial line because it minimizes the losses. A higher impedance demands a narrower central conductor whose resistance increases, a lower one reduces the wave impedance but this impedance reduces the losses when bigger. At low frequency (when the telephone transmitted at few kHz) magnetic material can reduce the losses by increasing the wave impedance. Impractical in UHF. A smaller dielectric constant also reduces the losses by increasing the wave impedance. Such cables have mainly air as an insulator, and little plastic to hold the central conductor. Their wave impedance can be (not always) 93ohm to keep the optimum diameter ratio. A higher impedance, like 300ohm, is impossible in a coaxial line. It exists for flat ribbons, which are by nature symmetric and unshielded.They can't replace coax cables as is, and unshielded cables are bad for TV, among others because echoes due to reflections on the landscape create image ghosts, which the antennas try hard to remove through directivity, and the cable should not pick up. In other words: excellent reasons made the 75 ohm standard, which is here to stay. Until you put the whole tuner right at the antenna, and then the cable can be an optics fibre if you wish.

300 transistors don't make a processor. Not even a 4004. I disapprove the hype in science papers, be it in Nature or elsewhere.

I'm interested in the diameter of the mirror. You told "reasonably extrapolated". How much?

Yes. An astronaut, a pebble... Phobos is still far enough from Mars - but not by much - to retain its integrity through its own gravitation. An orbit is more difficult, because it deforms over time du to Mars' influence, so I bet an orbit good enough would be very difficult. But that's only a guess, and there must be other possibilities serving the same purpose - say, an orbit formally around Mars that stays near Phobos and permits to observe Phobos from varied directions. Nasa, Wiki and many more reveal Mars' mass. It doesn't exactly need an explanation. Please feel free to provide us your estimate of the Sun's tidal effect near Mars. Hints: at Earth, the tidal effects of the Sun and our Moon are nearly as strong, Mars is farther to the Sun than Earth is, Mars is heavier than our Moon, and Phobos is much nearer to Mars than Earth to our Moon. And tidal effects vary as distance-3.

Where did you get this bizarre idea? Forget any philosophical or rhetoric approach of QM. Go to the maths.

Could you detail that? Presently I believe that rest mass plus kinetic enegy (plus other energies) define an object's inertia, which cannot differ from its gravitational mass. Arguments in messages 10 and 15 there http://www.scienceforums.net/topic/74526-q-on-general-relativity/ How would you enable one to determine an absolute speed through the gravitation created by the kinetic energy? He observes that an object moving with respect to him creates a gravitation field stronger that the rest mass would. I don't see an absolute origin of speed there. In case I was misunderstood: I mean that the moving object produces a stronger gravitational field as experienced by the observer how notices a speed. In the original example, the test mass and the scales move relative to Earth, so Earth produces a stronger gravitational field, and the scales indicate a bigger weight.

Yes, why? In addition, the measure setup isn't very good... It will give some notion of the impedance seen at the coaxial T, that is, through a length of coax. Passing by the preamp with a T right there, then going to the meter, would have fewer drawbacks; it would tell by how much the preamp's input shunts a 25ohm resistance. The generator probably shows an output impedance near to 50ohm resistive. The meter is more difficult to make resistive; it uses to be more accurate if the input is an attenuator with a mechanical switch. Anyway, this setup will not detail the resistance and reactance, which demand a vector meassure (0° and 90° components), as made by a network analyzer. But a measure of how good the matching is can be done with a reflectometer (a directional coupler) http://en.wikipedia.org/wiki/Power_dividers_and_directional_couplers without demanding a vector measure.

And you believed the tale of nanotube processor? I regret that the MIT technology review prints such titles.

Could you provide "reasonably extrapolated" figures about the mirror diameter - or other technology - that focusses light on a sail over an interstellar distance? And about the reasonaly extrapolated mean power of the laser?

In electronics, individual electrons are often observed directly. For instance at sensitive cameras, where the collected charge is multiple of q. Or in small MOS transistors, where the noise voltage is multiple of q/C where C is the grid capacitance. Less direct: noise amplitude depends on charges being a multiple of q. Easy to observe as well, for instance the noise voltage of a resistor, the noise current of some current sources.

You have written an equation for an oscillator without damping, so it never attains a stabilized state, and you can't ignore the transient solution. Especially, if you excite it at resonance, with a feeding system that doesn't weaken nor saturate (not feasible), then the energy will increase indefinitely. This corresponds to the energy provided by the excitation.

Maybe Sidarath means the relativistic correction, and then, yes, the scales show an increased weight at constant speed. The chosen case is difficult to observe because a high speed needs a big acceleration over a long path. Easier to observe is the kinetic energy of electrons in heavy atoms: this kinetic energy contributes to the atom's mass and weight, and is observable.

A matching resistor worsens the noise, and normally you shouldn't find any in a good preamplifier. Well, everything exists. This is fully acceptable if a preamplifier is near the antenna, and the television receives a strong signal, possibly at its mixer. Antennas use to be poorly matched because covering a wide band, like 470-860MHz, demands trade-offs.

The best option, if available, would be to join an astronomy club.

Yes, that' it, Hill sphere. The Roche limit is essentially the same if treating a non-deformable body, but astronomers define it versus the densities rather than masses, and seek the limiting distance to the more massive body. It boils down to the same condition. I certainly agree that any orbit so near to the limit wouldn't last. Though, pebbles just resting on Phobos would stay there, for being nearer to Phobos' center than the Lagrangian points L1 and L2 are - which is the case because only tidal forces from Mars act on them.

I've Iearnt something about the turbulators, thanks, +. I'm wary about public explanations of these torpedoes. The way I understand them: Friction has about no importance. They swim at 300+ m/s, it's all bout water inertia and cavitation. The bubbles are not a lubricant layer. Their tip is designed to produce a vacuum around the prow. At that speed, any enlarging section would produce a vacuum (or vapour, no importance); the design lets only the tip make one, so this bubble is but wider than the body instead of much wider, and may even reconnect with the body near the aft. Ideally it reconnects where the body converges again, to regain some forward push from the power invested in pushing the water outwards. To the least, the bubble collapsing there must wet the stabilizer, because hydrodynamic forces at the tip only would make the torpedo unstable. It must be very difficult (impossible?) to design a tip that works properly at every depth and speed. I suspect they adapt their length and shape actively. No gas has to be ejected to achieve a bubble. It is the natural consequence of speed. ---------- The only engine I imagine for such a speed is a rocket. It could have blown at the tip, but I feel it disadvantageous as it would further hamper the collapse of the bubble before the aft. At least in a first attempt, I'd put the rocket at the aft. Hydrogen peroxide is a rocket propellant that can also work alone. It's a quite dangerous one that often detonates without a known reason and may explain the Kursk disaster - or an other propellant. Other choices among liquids storable at room temperature aren't much better: hydrazine... Peroxide is long known for torpedoes as its decomposition exploited in a turbine served to rotate the propeller. Do I remember that its concentration is <70% then, which avoids its detonation? The choice of propellants would be the same dilemma as for launchers, made worse by the confined submarine room. I'd prefer to store cold liquid oxygen than explosive peroxide or toxic tetroxide and hydrazine - in a submarine even more. Solids might be an option as well, for instance nitrocellulose+nitroglycerine, if these torpedoes can have every time the same speed profile. I suppose bubble trails are no worry in such weapons.

Why TV tuners don't tell the input impedance? All the ones I've seen are meant for 75 ohm, the cable impedance that gives the minmum loss. So I imagine TV producers prefer not to worry the customers with that. In addition, matching a 75 ohm cable or source with a 75 ohm load makes very little difference in the power transfer (slightly more in the noise power, still negligible). Imagine a 1Vrms 50ohm source: a matched 50ohm load gets 5mW, a 75 ohm load 4.8mW, that is 4% less or 0.2dB. So just feed with 75 ohm. I've never seen a TV with a symmetric antenna input; such an input would be 300 ohm (seen 240 ohm on German FM sets, it makes no difference neither). If willing to measure a preamp's input impedance, -30dBm is about the maximum, -40dBm better.

OK, seen on the website of Alexander Schleicher's gliders turbulators meant to reduce the drag.

Compensing Mars' attraction forces is not necessary, because Phobos "falls" (orbits) freely in Mars' attraction. So this is not a case where Mars and Phobos are pinned to the floor and both attract a test mass in between, for instance a pebble at Phobos' surface to compare with the Roche radius. It is a case where Mars attracts the whole Phobos, and we wonder by how much the acceleration resulting from Mars is stronger at Phobos' surface than at its center of inertia, and whether the acceleration produced at Phobos' surface by its own mass can overwhelm it. So as a first correction, Mars acts only by its tidal effect. I write M, m the masses of Mars and Phobos, R the distance to Phobos, r the distance from Phobos to the questionable position. From GM/R2 the difference of attraction by Mars is r*2GM/R3 (write signs where you want if it helps you, here's a stock - - - -), to be compared with the full Gm/r2, which gives 2M/R3 = m/r3, or (r/R)3 = m/2M. With M=6.4e23kg, m=1.0e16kg R=9377km this brings us a first Roche limit of r=18.6km, slightly more than Phobos' biggest radius. A second correction (often included in the term "tidal effect") is that the centrifugal force also differs between Phobos' centre of inertia and the questionable position; it varies as r/R, and equates at the centre of inertia the attraction GM/R2, introduces again a r*1*GM/R3, so that the limit is now 3M/R3 = m/r3, or (r/R)3 = m/3M. Now r=16.3km, still a bit more than Phobos' biggest radius. This is for a moon in synchronous rotation (probable if we wonder about Roche's limit) and holds as well for the Lagrangian points L1 and L2 A computation at Wiki if someone finds it any understandable - they make it with density instead of mass http://en.wikipedia.org/wiki/Roche_limit the magic word "tidal" is in the first line of the "explanation" paragraph. This is for a stiff body; a deformable one is more complicated. This computation is exactly the same as for the Lagrangian points L1 and L2, these ones are less complicated at Wiki http://en.wikipedia.org/wiki/Lagrangian_point

Oops. Well, the methods are the same. Do not overload the preamp; odBm is already an important signal for it. The hidden question is: a well-made preamplifier is NOT optimum when its input impedance matches the cable, because apart from getting the maximum input power, it must also create the minimum noise, which does not happen at impedance matching. The minimum noise is when the driving resistance is the ratio of the preamplifier's noise voltage and noise current, and the susceptances of the soure and preamp compensate. - The optimum impedance is between the source matching and the minimum noise. The impedance mismatch is easily 2:1. - This optimum impedance is impossible to reach over such a wide band, and difficult even over 470-860MHz. - 50 to 800MHz covers two VHF TV bands and one UHF (split in two usually). The TV's input probably has a 2 or 3-way filter feeding as many preamplifiers, so a random impedance between the bands would be absolutely normal, and even desireable to attenuate outband noise. - You get the optimum generator impedance (hence the optimum preamp impedance seen by the generator) in the datasheet of the preamplifier transistor (...or tube, I've seen the last ones). The manufacturer uses to give a noise figure and an optimum impedance in VHF and UHF+, rather than a voltage and current noise in LF. Still feeling a need to measure it?

----- Samples boxes ----- Many boxes shall separate the samples and keep them clean - in vacuum like on the Moon. Though, the mass of the boxes competes with the samples, or alternately, the box mass fraction determines the mission launch mass. Milled aluminium, with thin walls and stiffeners, would make boxes 3 times as heavy as the samples, so here's a lighter design. The walls and cap are electrodeposited of Ni or Ni-Co. For a D=80mm box, 100µm let the bottom resist >3bar, the walls as well if corrugated by 3mm peak-to-peak (if I didn't botch it), and the cap is slightly thicker. A box 200mm long weighs 80g, two 60mm pebbles in it 560g. A Ni sandwich is possible, especially with balsa wood plus syntactic foam, but bare Ni eases cleaning and sterilization. Solder shall seal each filled box, for instance fluxless Sn-Pb-Ag. The mating faces are covered with readily wettable Sn, surrounded by rings of non-wettable material (like anodized Cr) to contain the solder, which is pre-applied on both parts. The prospector can use a funnel to pour or drop the samples more cleanly, it has varied brushes anyway, and may remove some dust-protection layer or part. Then it applies the cap on the box and remelts the solder by induction with a ring coil half-surrounded by laminations. A different process tightens food tin cans: possible source of inspiration. The prospectors have boxes of several sizes to optimize the volume and mass. Samples that resist crushing can travel in a simpler bag made of two swollen sheets of Ni welded or brazed at three sides; after filling, the prospector folds strongly the fourth side and solders its tip. Such bags are even lighter, like 15g for 300g samples; I'd let them travel as bulk. Bags and boxes have non-removeable identifications - readable in 50 years please, hence with the naked eye. The boxes and bags need a high emissivity: maybe an anodized coating of Cr. I like bare Ni as the inner face, but some boxes or bags can have Cr, Au, Ta, ceramic... coating for contamination double-check. ---------- Boxes hold permanently at 45° by polymer or metal straps at a central truss, building a magazine, with the bags dumped at the truss' middle. Arbitrary 60kg samples per prospector would occupy about D=0.8m H=1.0m. A D=0.6m 6-node truss that breaks at 50kN (50g during atmospheric re-entry) can consist of 340mm*17mm*0.5mm welded AA7020 tubes and weigh 3.5kg. An mobile impact protection is necessary at Moon landing, lift-off, and rendez-vous with the ferry. Thin aramide sandwich weighs 3kg. Arbitrary 60kg samples per prospector then need 9kg bags, boxes and straps, 4kg mobile truss, 3kg protection, or 300g per kg of samples - without the prospector's tools. A second vacuum barrier protects the samples. This one shall wait on Lunar orbit, and be the atmospheric reentry capsule. Marc Schaefer, aka Enthalpy

Evaporation does cool the liquid, BUT for air conditioning you need <<+30°C, possibly +15°C at the liquid, and then the vapour pressure is tiny. My gut feeling is that compressing the vapour then to obtain the liquid gets costly. Climatisers use to produce condensation water from the air. This water isn't very clean.